using System;
using System.Collections;

namespace Org.BouncyCastle.Asn1.X509
{
	/**
	 * The DigestInfo object.
	 * <pre>
	 * DigestInfo::=Sequence{
	 *          digestAlgorithm  AlgorithmIdentifier,
	 *          digest OCTET STRING }
	 * </pre>
	 */
	public class DigestInfo
		: Asn1Encodable
	{
		private readonly byte[] digest;
		private readonly AlgorithmIdentifier algID;

		public static DigestInfo GetInstance(
			Asn1TaggedObject	obj,
			bool				explicitly)
		{
			return GetInstance(Asn1Sequence.GetInstance(obj, explicitly));
		}

		public static DigestInfo GetInstance(
			object obj)
		{
			if (obj is DigestInfo)
			{
				return (DigestInfo) obj;
			}

			if (obj is Asn1Sequence)
			{
				return new DigestInfo((Asn1Sequence) obj);
			}

			throw new ArgumentException("unknown object in factory: " + obj.GetType().Name, "obj");
		}

		public DigestInfo(
			AlgorithmIdentifier	algID,
			byte[]				digest)
		{
			this.digest = digest;
			this.algID = algID;
		}

		private DigestInfo(
			Asn1Sequence seq)
		{
			if (seq.Count != 2)
				throw new ArgumentException("Wrong number of elements in sequence", "seq");

			algID = AlgorithmIdentifier.GetInstance(seq[0]);
			digest = Asn1OctetString.GetInstance(seq[1]).GetOctets();
		}

		public AlgorithmIdentifier AlgorithmID
		{
			get { return algID; }
		}

		public byte[] GetDigest()
		{
			return digest;
		}

		public override Asn1Object ToAsn1Object()
		{
			return new DerSequence(algID, new DerOctetString(digest));
		}
	}
}
